In the drilling of wells, drilling mud is pumped through a Kelley or driver at a pressure sufficient to flow down through the interior of the drill string to the bit at the bottom of the string and then upwardly through the annulus between the string and the wall of the bore hole.
From time to time, the pump is stopped and the drill string is disconnected from the Kelley or driver, for example, to add or remove pipe sections from the string, or to replace the bit, which requires pulling the entire string. A considerable amount of drilling mud remains in the Kelley and can flow or drain from the lower end of the Kelley each time it is disconnected from the drill string.
Mud draining from the kelley often spills on the floor of the drilling rig and causes unsafe conditions for workmen, and can also cause pollution and environmental problems if the mud spills on the ground. Time is lost because it is usually necessary for the workmen to wait until the mud has drained from the kelley before another connection can be made to the drill string, and the mud lost is expensive.
Kelley or mud saver valves with a flexible tubular body or diaphragm, which opens in response to pump pressure, and closes automatically under the action of compressed fluid such as a pressurized gas, in a chamber surrounding the body are known, as described for example, in U.S. Pat. No. 4,303,100. While the valve of Patent 4,303,100 may operate satisfactorily when drilling relatively shallow wells of a few thousand feet, the diaphragm is damaged at the very high pump pressures required for deep drilling. Such high pump pressures extrude the diaphragm material through the small openings in the back up sleeve and the diaphragm either punctures or fastens itself to the backup sleeve so it will not close when pumping pressure is again released.
In our copending U.S. application Ser. No. 410,889, filed Sep. 22, 1989, the disclosure of which is incorporated herein by reference, a support for the diaphragm has openings facing the diaphragm, and there is a backup element behind the support. As the mud pressure increases, the diaphragm is forced toward the support, pressurized gas escapes through the openings and then through a small clearance space between the support and the backup element, and the diaphragm seats on the support. As pump pressure further increases, the diaphragm forces the support against the backup element to close the clearance space so the diaphragm material cannot extrude through the openings in the support.
Each time the mud pump is started, the mud pressure increases almost instantaneously to the full pumping pressure. When drilling a deep well, this pressure is several thousand psi, and the initially closed diaphragm is subjected to this very high pressure instantaneously and is slammed against the support. It is believed that from time to time, when the pump is started, the openings in the support are closed by the diaphragm before all the pressurized gas can escape from between the diaphragm and the support. The resulting gas pockets behind the diaphragm in the regions between the openings weaken the diaphragm. At high pump start-up pressures the diaphragm is believed to act like a flexible stopper which closes the openings before all the gas can escape. While the gas pockets can be minimized by increasing the number of openings, and/or changing the locations of the openings, additional machining is required, and a better solution has been found.